The goal of the proposed research is the study of the biology, and particularly the behavioral genetics of obesity. The guiding theme is that obesity provides an ideal model system for the study of gene-environment interactions. This theme will be studied by a variety of approaches. A major effort will be invested in further exploitation of our Danish Adoption Study data, including the analysis of data already collected on siblings and half-siblings, a path analysis of the entire data set, a preliminary analysis of major gene involvement by mans of commingling analysis and a study of the childhood weight patterns of the adoptees. A second major effort will be devoted to studying weight changes in depressed people, seeking increased understanding of both obesity and depression. A large-scale family study in Argentina will attempt to define the risk of obesity of first degree relatives of obese persons. Another study will assess the value of body fat distribution in predicting the occurrence of gestational diabetes. We will also attempt to follow up a group of English children of normal weight who had been identified ten years ago as being at high and low risk for obesity. One study will assess the effects of a gastric "Bubble" (balloon) on the regulation of body weight, uncontaminated by the behavioral treatment programs that are usually required to be associated with this intervention.